This invention relates to a height measurement apparatus using a laser light beam.
In some of height measurement apparatus, a laser light spot is applied to a surface of a measured object, and the applied laser light is reflected at the surface of the object before entering an optical position sensor. A position at which the reflected laser light meets the optical position sensor depends on the height of the surface of the object. The optical position sensor outputs an electric signal depending on the position exposed to the reflected laser light. Thus, the output signal of the optical position sensor represents the height of the surface of the object.
U.S. Pat. No. 4,589,773 discloses a similar height measurement apparatus.
Such a height measurement apparatus can be used in a system for inspecting solder portions of a circuit board as suggested in U.S. Pat. No. 5,103,105. It should be noted that U.S. Pat. No. 5,103,105 is not prior art to this invention.
As will be explained later, a prior-art height measurement apparatus has some problem.